Traditionally, acoustic enclosures such as loudspeaker systems are designed without a way to actively monitor sound pressure and other acoustic conditions within the enclosure during operation. Actively monitoring sound pressure within an acoustic enclosure can help determine the current state of an acoustic system within the enclosure and whether the sound quality within is being optimized. The relatively high acoustic pressures generated inside a loudspeaker can be measured directly by a microphone with a sufficiently high pressure tolerance. However, pressure tolerant microphones are typically expensive and difficult to calibrate making it both costly and complex to actively monitor pressure conditions from within acoustic enclosures.
FIGS. 1A-1C are cross-sectional views depicting various implementations of a conventional loudspeaker system known to those in the art. FIG. 1A depicts a sealed loudspeaker system 151a having a housing 152a formed of one or more contiguous surfaces arranged to enclose a hollow, three-dimensional chamber of a certain size and shape such that it possesses the desired acoustic properties. An active driver 154a is driven by corresponding electronic control circuitry (not shown). An active driver may alternatively be referred to as an electroacoustic transducer, or simply a speaker.
FIG. 1B depicts an additional example of a loudspeaker system 151b. FIG. 1B contains all of the features discussed with respect to FIG. 1A with the addition of a port 156 disposed in the housing 152b. The dimensions or location of the port 156 may be sized such that it provides desired levels of acoustic resistance and reactance to the acoustic energy propagating through the loudspeaker enclosure. The addition of a port 156 may, for example, enable the loudspeaker to produce lower frequency sounds at higher fidelity and with less driver distortion.
FIG. 1C depicts an additional example of a loudspeaker system 151c. FIG. 1C contains all of the features discussed with respect to FIG. 1A with the addition of a passive radiator 158 further disposed in a surface of the housing 152b. Passive radiator 158 has a diaphragm capable of vibrating similarly to active driver 154c. Unlike an active driver 154c however, passive radiator 158 is not electrically driven and instead vibrates in response to the sound pressure inside the loudspeaker produced by active driver 154c. The sizing, positioning, and materials used to construct passive radiator 158 are selected such that passive radiator 158 provides a specific level of acoustic resistance or reactance to achieve a desired frequency response. A passive radiator 158 may, for example, provide similar benefits as a port 156 while occupying a smaller volume within the loudspeaker enclosure. A passive radiator 158 may have an adjustable acoustic mass so that the amount of acoustic impedance it provides may be tuned.
It is appreciated by those in the art that a conventional loudspeaker system 151a-151c may include any number of active drivers 154a-154c, ports 156, passive radiators 158, or other conventional loudspeaker components necessary to achieve the desired frequency response and other acoustic properties.